Considering the amount of LEDs that reside in the warp nacelle and to prevent light "bleeding" into areas where it's not supposed to I came up with this! A blue LED sits atop this construct, with two more in the rear section. (still got to figure that part out...)
You can use shrink tubing on LED's to cut down on the side lighting leaking. The tops can be polished or cut at an angle, then polished too, as long as you don't expose the Cathode and Anode.
There's a cardboard inner that takes care of most of the leaks in the nacelles. I also build "light-boxes" to mount the LEDs. If you look at some of the earlier pictures you can see some of my "light-boxes" (Shuttle bay, rooms in saucer section)
Then Zathros' suggestion of heat-shrink tubing around the LED works really well, lastly pre-stik to patch in small holes & tricky bits. Or blu-tack. Don't know what you call it the US
Struggled a bit with warp nacelle alignment, I think I compromised the design with the additional weight in the nacelles and cutting through supports for the wires
Now, an interesting excercise in scale; both my Voyager and Enterprise are listed as 1:400
Now, according to various sources Voyager is 334m long, Enterprise 304m. So, we can see the problem, these two models should be about the same size! For the record, the Voyager model is 42cm and Enterprise 72cm. Methinks (it's late, I'm not doing maths now...) that Voyager is actually 1:800....